1. Field of the Invention
This invention relates to a ceramic welding repair process. Ceramic welding repair processes are useful inter alia for the repair of hot refractory structures such as furnaces or ovens of various kinds, and they enable eroded areas of the refractory structure (provided that those areas are accessible) to be repaired while the structure is substantially at its operating temperature and in some cases even when the structure is still operating.
2. Description of the Related Art
In ceramic welding processes, refractory powder, fuel powder and oxidising gas are projected against the site to be repaired and the fuel is burnt so that the refractory powder becomes at least partially melted or softened and a refractory repair mass is progressively built up at the repair site. The fuel used is of a nature that it can form a refractory oxide on combustion, and typically consists of silicon and/or aluminium, though other materials such as magnesium may also be used. The refractory powder is typically selected so that the chemical composition of the repair mass matches as closely as possible the composition of the refractory to be repaired, though it may be varied, for example so as to deposit a coating of a higher grade refractory on the base structure. In usual practice, the fuel and refractory powders are projected from a lance as a mixture in a stream of oxidising carrier gas.
Due to the intense heat liberated on combustion of fuel powders which form refractory oxides at or close to the surface to be repaired, that surface also becomes softened or melted, and as a result, the repair mass, which is itself largely fused together becomes strongly adherent to the repaired wall, and a highly effective and durable repair results. An early disclosure of ceramic welding repair techniques is to be found in British Patent No. 1,330,894.
Such known techniques give very good results when applied to large plain wall areas such as are encountered in coke ovens and in the vaults of glass furnaces, and they are also very useful for the repair of rather large openings in walls, such as dog house arches and burner ports of glass melting furnaces. By suitable choice of lance outlet, such techniques may be adapted for the repair of smaller openings, such as the tap holes of, for example, basic oxygen (L-D) steelmaking furnaces which typically have a diameter of about 20 cm, see for example British Patent Specification No. GB 2 144 055 A.
There is however a problem involved in the repair of refractory wall areas which contain smaller openings, for example below 10 cm, where it is not really practicable to insert a lance into the opening with sufficient clearance to manipulate it to effect the required repair. Typical examples of such small openings are tuyere openings for the introduction of air or other gases, or indeed powdered material such as carbon powder, into tanks for various purposes, such as in copper, zinc and other metal converters, basic oxygen steelmaking furnaces, blast furnaces, gas burner blocks (e.g. side ports) in glass furnaces and submerged openings provided for the introduction of electrodes into a melt, for example in a glass furnace or for bubbling a gas through a melt. It is an unfortunate fact of life that because of the excitement of the melt by the introduction of gas or other material, or by the concentration of electric current at the location of the openings, the areas of the refractory wall immediately surrounding such openings are often among the most readily eroded in the furnace.